Superheater construction and arrangement



May 20, 1958 c. GUARRAIA 2,835,479

SUPERHEATER CONSTRUCTION AND ARRANGEMENT Filed Aug. 18. 1953 2 Sheets-Sheet 1 Fig. 2.

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INVENTOR.

. Charles Guorruio BY M ATTORNEY Temperature F May 20, 1958 c. GUARRAIA SUPERHEATER CONSTRUCTION AND ARRANGEMENT Filed Aug. 18-. 1953 3A. 850 23? F lOOOtF Avg.

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Superheoter 35 Front Channel I200 Furnqce Rudiuflon 0I23456789|O||I2|3l4l5l6 IIVVE/VTOR Loop Number of Final Section Fig. 3.

Charles Guarruiu BY ATTORNEY 2 Sheets-Sheet 2 ite States S'UPERHEATER CONSTRUCTION AND ARRANGEMENT Charles Guarraia, Hawthorne, N. 37., assignor to Combustion Engineering, Inc., New York, N. Y., a corporation of Delaware Application August is, 1953, Serial No. 375,005 8 Claims. or. zsv zrrs The present invention relates to vapor superheaters. that absorb heat by the flow of combustion gases thereover and particularly to an improved arrangement of the heat absorbing elements of a high temperature steam superheater so as to reduce the cost of the elements exposed to furnace radiation and the high temperature gases.

T o attain the high steam temperatures required today in power plants, it is often necessary to utilize costly high temperature steels in at least a portion of the superheater elements for the parts thereof exposed to furnace radiation. These conditions also frequently require for safety reasons the use of thicker walled tubes in these locations. All of these considerations lead to the increase in cost and weight of the superheater.

The present invention contemplates overcoming the aforesaid disadvantages by distributing part of the surface of a convection superheater so that those elements which are exposed to furnace radiation are arranged so that they are traversed by steam at lower entering temperature, higher velocity, and in greater quantity than other superheater elements. These particular elements have a shorter steam flow path than the majority of the superheater elements with the result that the steam temperature is lower, the rate of flow therethrough is accelerated and consequently the amount of steam traversing is increased with respect to that of the other elements.

The invention will best be tmderstood upon-consideration of an illustrative embodiment thereof when read in conjunction with the accompanying drawings in. which:

Figure l is a schematic elevational view of a convection type superheater arranged in a gas pass at the outlet of a furnace in accordance with the present invention.

Figure 2 is a diagrammatic plan view of the superheater; and

Figure 3 is a chart illustrating the temperature conditions of the metal of the superheater elements and also the steam passing therethrough as compared with corresponding conditions in conventional arrangements.

Figure 3A is a schematic illustration of the tube parts for which temperatures are shown in Figure 3.

in Figure l the numeral designates a gas passthrough which high temperature gases, as from a boiler furnace 21, flow over superheating elements in the direction of the arrows or from left to right in the figure. The numerals 22 and 22A designate the upper and lower walls or boundaries of the gas pass 20 outside ofwhich are located the superheater inlet header 28 and the outlet header 29. The superheater elements comprise lengths of tubing which are sinuously bent to provide a plurality of contiguous generally U-shaped loops 23, 24, 26, 27. A

number of these sinuously looped single elements are.

superheater sections (designated by letters A to L etc.)

are distributed substantially uniformly across the entire Patented May 2%, 33523 width of the gas passage so that all of the twelve sections across the pass 20 near its exit are subjected to the heat of the gas at substantially the same temperature. Approxi- 'mately midway of the length of each superheater section mediate loops of the six combined sections A, C, etc.,

are similarly offset to right and left further along the pass so that the legs 27a and 27b of the loops create the final three sections A E and 1 each having the loops thereof located in a single plane. In the form shown, the last U-loop 27 is reversed so that the outlet legs 27a of the U-loops lie downstream in the gas pass with respect to the upstream legs 27b of these loops. However, if de sired, all of the loops might be similarly formed so that the portions 27b of the last loops would lie to the left of the portions 27a thereof as is the case with the other loops.

In addition to sinuously formed elements which have loops 23-26 inter-nested as described above, each section A-L of the superheater includes at least one element 30 which has several U-shaped loops 31, 32, 33 formed therein to be nested with a corresponding number of the loops of other elements of this section skipping the initial loops 23 and an intermediate loop 26 of each section. Intermediate parts 35 of these elements 30 which are not formed with as many sinuous loops throughout their length as in the remaining elements extend along the gas path without nesting with loops of the other elements therein and may if desired be projected through a boundary wall of the passages and extend along the axis of the gas passageoutside the latter. In portions adjacent their outlet ends the elements 30 are brought back into the gas pass, if partly outside, and formed with loops 33 embracing the loops 27 of the other elements so that legs 36 thereof extend in spaced parallel relation and in the plane of the legs 27b of the remaining elements so as to lie between the furnace 21 with the radiation from the latter and legs 27b.

The elements 30 having few loops are shorter in length than the remaining elements of the various sections and consequently the steam entering the front portions 36, will be at a lower temperature than in the remaining elements. In addition, the steam from the inlet header 28 to the outlet header 29 will be in greater quantity. As a result, the steam and metal temperatures throughout these front (screening) portions 36 will be considerably lower and will not reach the excessively high levels present in the conventional designs. Thus it is possible to make these elements of more economical steels so that the expense of utilizing expensive alloy steels is eliminated.

Because of the combining of several initial sections into asingle final section (four into one) as described above, each of the final sections will include four tubular elements 30 which are of shorter length with their end portions 36 located upstream in the gas pass 2% with relation to the remainder of the superheater tubes of a section in this high temperature zone, one of these portions 36 coming from each of four initial sections as A to D which combine first into two sections A, C and then these adjacent sections are merged to form a final section A These four final parts of elements 30 are designated 1 to 4 in Figure 3, and are located closest to the furnace.

In Figure 3, the graph M indicates the temperature of the metal at the point X (Figure 3A) of the final loops of superheater elements in each section. The ordinate of the graph represents temperature in degrees Fahrenheit, while the abscissa represent the sixteen tube parts from various sections that are combined into a single section at the high temperature zone. For purposes of comparison, the graph N is provided to illustrate the tem-' perature conditions that would exist under like conditions in the metal of a conventional similarly located superheater at the mid-point X of the final loops. The graphs S and T similarly represent the temperature of steam leaving the several elements while the graphs U and W represent the temperature of steam entering these elements. From the graphs M and N it will be seen that the metal temperature in the portions of the elements marked 1 to 4 in Figures 3 and 3A most exposed to radiant heat is substantially reduced because of the lower steam temperature, greater quantity and higher velocity of steam flowing through these elements 30 due to their shorter length, As compared with an expected temperature condition of 1173 F., that would otherwise exist at the midpoint of the final loops of conventional elements the parts 1 to 4 would be at approximately 1083 F. Thus, an average outlet steam temperature of say 1000 may be attained without the necessity of exposing the metal of all elements to such high temperature conditions as would require the employment of costly steel or thick walled tubes. The steam entering the portions 36 of the elements 30 is lower as shown for elements 1 to 4 in graph U than that in the other parts of the final loops of the superheater and thus protects these parts. Nevertheless, the steam temperature rise or pickup in these elements is greater primarily due to furnace radia tion than in the other elements as may be seen by noting for each element 1 to 4 of the final loops the distance between the lines U and S on the graph as compared with the distance between these lines for the elements 5-16. Furthermore, although the temperature of the steam at the outlet of the elements 1 to 4 is less at 940 to 990) than that of conventional elements at these cations (at 10l0 to 1070), the same average temperature for steam from all of the elements of the final section is attained as with the conventional elements. A final temperature of say 1000 may be attained with the present arrangement while to attain the same steam temperature with conventionally arranged elements would involve subjecting the element parts nearest the furnace to temperatures which are impossible for use with present steels; even presently possible steam temperatures would require the utilization of expensive alloys or thickwalled tubes, both of which are costly expedients.

What I claim is:

1. A superheater located in a gas passage opening directly out of a furnace comprising; a group of heat absorbing elements connected between a supply header and a collecting header having tubes spaced longitudinal- 1y of the gas passage and connected serially for flow of steam therethrough with parts of said elements exposed to direct radiation of heat from said furnace; and other tubular elements in said passage of shorter length extending from the supply header to the collecting header and including tubular parts which absorb less heat in the gas passage than said first elements with portions of said other elements interposed between the furnace and all tubular parts of said group of first mentioned elements exposed to radiation from the furnace, whereby the part 'of the superheater closest to the furnace includes tubular elements receiving steam at different temperatures with the tubular element portions receiving steam at the' 4 said passage of shorter length between the supply header and collecting header and including tubular parts which absorb less heat in the gas passage than said first elements with portions of said other elements interposed between the furnace and said entire group of first elements in the same plane, whereby the part of the superheater closest to the furnace includes tubular elements supplied with steam at different temperatures with the tubular element portions 1 receiving steam at the lowest temperatures being located closest to the furnace.

' 3. A superheater located in a gas' passage opening directly out of a furnace comprising; a plurality of internested tubular superheater elements connected between supply and collecting headers for counterfiow of steam with respect to gas flow in said passage, each element being sinuously formed with a plurality of contiguous U-shaped loops spaced in the general direction of gas flow and inter-nested with other similarly formed elements; and other superheater elements in said passage connected between said headers and formed with a lesser number of sinuous loops than said first elements and inter-nested with a like number ofloops of the latter with portions of said other elements by-passing certain loops of said first elements to nest with loops thereof that are closest to said furnace.

4. Apparatus for superheating vapor comprising; means forming a passage for the flow of hot gas in a stream extending throughout the entire width of the passage; a superheater for vapor under pressure having a plurality of separate sections distributed substantially uniformly across the entire width of the passage so that all of the sections are subjected to the heat of the gas at substantially the same temperature, each superheater section comprising; a tube bent into sinuous form to provide a series of loops of generally U-shape with a plurality of such elements intermeshed to form panels located in uniformly spaced relation across said gas passage, said sections spaced across the passage being progressively merged at intervals in the gas passage into lesser numbers of more widely spaced sections so that the final sections each have loops of tubular elements from a number of the initial sections spaced across the gas passage and include loops of tubular elements, from a number of sections, which are of shorter length than the remainder of said internested elements.

5. In a boiler having a furnace, and superheater elements connected between a supply header and a collecting header and so disposed with respect to the furnace outlet that portions of said elements adjacent the furnace are exposed to the direct radiation of heat from the furnace; other superheater elements of shorter length extending from said supply header to said collecting header and absorbing less heat from the gas flowing from said outlet with parts of said other elements located between the entire extent of said radiantly heated portions of said first mentioned elements and the furnace, whereby the part of the superheater closest to the furnace includes element portions receiving steam at difierent temperatures with the I element parts receiving steam at lowest temperature being located closest to the furnace.

6. In combination with a furnace and superheater elements connected between a supply header and a collecting header and so disposed with respect to the furnace outlet that portions of said elements adjacent the furnace are exposed to the direct radiation of heat from the furnace; other superheater elements of shorter length extending from said supply header to said collecting header and absorbing less heat from the gas flowing from said outlet with parts of said other elements receiving fiuid at lower temperature than said first-mentioned element portions and located between the entire extent of said radiantly heated portions of said first mentioned elements and the furnace to intercept the greater part of the radiant heat from the furnace and absorb it to raise the temperature of the cooler fiuid passing therethrough to substantially the same temperature as the fluid flowing through said first mentioned element portions.

7. In combination with a furnace and superheater elements connected between a supply header and a collecting header and so disposed with respect to the furnace outlet that portions of said elements adjacent the furnace are exposed to the direct radiation of heat from the furnace; other superheater elements of shorter length extending from said supply header to said collecting header and absorbing less heat from the gas flowing from said outlet with parts of said other elements located between the entire extent of said radiantly heated portions of said first mentioned elements and the furnace to intercept the greater part of the radiant heat from the furnace and absorb it to raise the temperature of the fluid passing therethrough to substantially the same temperature as the fluid flowing through said first mentioned element portions.

8. A superheater located in a gas passage opening from a furnace having sinuously looped tubes arranged to form groups of internested loops that are spaced relative to the direction of gas flow in upstream, intermediate and downstream groups with the inlet of the superheater being connected to the group furthest downstream relative to the gas flow and the outlet connected to the furthest upstream group; other sinuously looped superheater tubes interconnecting said inlet and said outlet with loops thereof spaced in the direction of gas flow and internested with fewer than all said loops of said first tubes and having portions of one loop thereof disposed upstream of the loops of said furthest upstream superheater group.

References Cited in the file of this patent UNITED STATES PATENTS 2,009,883 Frank July 30, 1935 2,033,077 Kerr et al Mar. 3, 1936 2,477,950 Bailey Aug. 2, 1949 

